Sound powered phone



July 21, 1959 A. H. KETTLER souuu POWERED PHONE Filed Nov. 2. 195;

INVENTOR Alfred 4/. Kef/cr Stats The invention relates to sound translating apparatus, and, more particularly, to noise-cancelling microphones.

One of the difficulties commonly experienced with sound-powered phones, such as are used at shipboard battle stations and other places, is that background noises, or ambient disturbances of engines, etc. frequently are reproduced along with the directed speech signal, and unless special means are provided to reduce or cancel these noises, the signals may well become unintelligible. One of the more elfective noise-cancelling means is to permit the sound Waves of the ambient disturbances to enter into the microphone from behind or to the rear of its diaphragm, the result of such an arment being that the disturbance sound Waves impinging directly on the outer surface of the diaphragm then are counteracted by the action of the same waves on the rear diaphragm surface. Microphones utilizing such a principle commonly are referred to as noise-cancelling phones, and, for the most part, they have been found reasonably satisfactory under normal operating conditions or circumstances.

They are not, however, as satisfactory in cancellingout sound disturbances which have an unusually high frequency or short wave. Further, in many of these instruments, the use of the noise-cancelling principle itself gives rise to attendant difiiculties in that, for example, their transducer mechanism normally must be sealed off and protected from the ambient and, to accomplish this, a space or chamber normally is formed behind the diaphragm. The difliculty arises from the fact that this chamber frequently is of such a volume as to give rise to objectionable standing waves resulting from ambient disturbances which are admitted to the rear of the diaphragm.

A further difficulty encountered in noise-cancelling microphones is their low sensitivity level which frequently fails to produce a clear signal even when excessive background noise is not present, the result being that amplifiers usually must be employed to render these instruments suitable for practical application in communication systems.

It is, therefore, an object of the present invention to provide a noise-cancelling microphone in which the sound translating mechanism is unusually sensitive and also is protected to a maximum degree against interferences and injury.

A further object is to provide a noise-cancelling, soundpowered microphone of a type which employs a diaphragm connected to an armature by means of a drive rod in which substantially the entire length of the drive rod and the armature is protected against outside interference.

These and other objects will become apparent from the accompanying drawings and detailed description.

According to the invention, the microphone employs, a somewhat conventional motor which may be formed of an armature, a coil, suitable pole pieces, a diaphragm and a drive rod operatively connecting the diaphragm to the motor. The drive rod, preferably, is permitted to be as long as conveniently possible and it extends from the atent ice 2 cal injury. This partition wall, in addition, forms an air chamber between itself and the diaphragm and, if the microphone utilizes the noise-cancelling principle, openings are provided from atmosphere into the chamher to admit disturbance sound waves so that they may act upon the rear surface of the diaphragm as well as on its front. One particular feature of the invention is that this portion of the partition wall, through which the drive rod extends, is projected into close proximity with the diaphragm, so that only a minimum portion of the drive rod extends through the noise-cancelling chamber. This projection is most beneficial in that it substantially reduces the volume of this chamber behind the diaphragm and thus minimizes such objectionable standing waves as are otherwise present in the conventional microphones.

As a preferred practice, the partition wall is rigid in structure and conical in shape, the apex of the cone projecting into close proximity with the diaphragm. Further, it is desirable to seal the opening through this apex with suitable gasketing mounted on the drive rod and such a sealing member provides the sole support for the extent of the drive rod between the diaphragm and the motor armature.

A further feature of the invention is the provision of a rotatable shutter member provided with spaced openings and adapted upon rotation to align its openings with other openings provided in the casing of the microphone. Upon alignment, atmosphere is admitted behind the diaphragm, but the more important function of the shutter is that its rotation also is capable of progressively closing off these openings so that sensitivity can be adjustably increased when background disturbances and noises are not an appreciable factor.

The preferred embodiment of the invention is illustrated in the accompanying drawings of which Fig. l is a longitudinal central section through the microphone and Fig. 2 another section taken along the broken line II-II of Fig. 1.

Referring to the drawings, the functional parts of the microphone are enclosed in a casing 1 which, as will be subsequently pointed out, is formed of a number of fitted-together parts, these functional elements including primarily a diaphragm 2 operatively connected to a motor armature 3 by a drive rod 4. Armature 3 projects downwardly from the drive rod into a coil 6 which, in turn, is surrounded by a plurality of pole pieces 7 supported in a suitable molding 8 that is mounted and secured in an inner casing or housing member 9 clamped and bolted in position in the manner shown, or in any other suitable manner desired. Further, the upper rear portion of casing 1 mounts a conventional plunger mechanism 11 adapted upon depression to energize the coil by closing switch 12. As might be expected, the circuitry of the present apparatus, as well as the structural support for the coil pole pieces, does not form a part of the present invention, and, since these elements are clearly shown in the drawings, it is not felt that a detailed description of them is necessary or even appropriate.

From an inventive standpoint, the more important elements of the invention concern themselves generally with the physical configuration of the transducer housing in relation to the diaphragm, as well as with the provision motor through an opening formed in a partition wall that acts to separate the coil mechanism from outside disturbances and to protect these mechanisms against physiof noise-cancelling means for the microphone. The noisecancelling means, broadly, is provided by forming a noisecancelling chamber 13 between a conical partition wall 15 and diaphragm 2, the purpose of this chamber being to permit sound waves of background noises to act upon the rear face of the diaphragm, and consequently, to cancel out their counter-part sound waves which simultaneously act upon the opposite face. Generally, noisecancelling chamber 13 is formed between diaphragm 2, wall 15 and an outwardly-projecting ring member 14 which has an inwardly projecting flange 16 provided exteriorally with threads adapted to mesh with a mouthpiece 20. Further, as may be seen in Fig. 2, ring 14 is provided witha plurality of circumferentially spaced radial openings 17 adapted to admit disturbances into chamber'lS and, most suitably, a shutter 18 is rotatably mounted on ring 14 to close 011 openings 17 as desired. For this purpose, shutter 18 is formed with openings 19 which, upon rotation of the shutter, align with openings 17. Thus, these outside, or ambient, waves may be admitted into the chamber or sealed off simply by adjusting the shutter. A coupling ring 21 threadably securedrto the casing may be used to retain the shutter, and, as shown, ring 21 is formed with a radially, extending flange engaging another ring member 26 which, in turn, has a shoulder 27 adapted to press against a radial flange 28 formed on shutter 18 to permit relatively free rotation of shutter 18. To facilitate rotation of the shutter, small roller bearings 29 are mounted between shoulder 27 and radial flange 28. Also, diaphragm 2 is secured in a clamped engagement between ring 14 and mouthpiece 20 and the mouthpiece is provided with a plurality of openings 22 through which directed speech signals travel to the diaphragm.

Another feature of the invention is the manner in which drive rod 4 is mounted and protected. To appreciate this feature, it first should be understood that sound waves acting upon diaphragm 2 are converted into mechanical movement of drive rod 4 which, in turn, is translated to armature 3 for varying the magnetic fields surrounding the coil and producing a signal that can carry to receivers located at remote points. Because of this, it is highly important that drive rod 4 be unusually sensitive to movements of the diaphragm, but, as also can be surmised, such a drive rod also will be highly sensitive to mechanical restraints present in chamber 13. It is, therefore, important to protect the drive rod as much as possible against such restraints and, in the present invention, this protection is provided by extending a portion of partition wall 15 into close proximity with diaphragm 2. With such an arrangement, only a mini-' mum portion of the drive rod projects through chamber 13, the result being that only a minimum portion of the drive rod is unprotected and capable of being affected by disturbances as well as by injurious outside conditions, such as salt spray, dirt, etc. Most suitably, partition wall 15 is rigid and is conical in shape with the apex of its cone projecting into proximity with the diaphragm. Also, drive rod 4 extends through an opening provided in this apex and a suitable sealing member, such as gasket 23, is utilized to further assure protection. The use of the conical partition wall not only provides maximum protection for drive rod 4, but, in addition, it permits an unusually long extent of the drive rod between the apex of conical wall 15 and armature 3. A drive rod supported in this manner is more effective in translating speech signals to a motor located as remotely as possible from the diaphragm. Yet another advantage to be gained through the use of the conical partition wall is that the angle of the wall is so disposed as to direct sound waves entering through openings 17 in the general direction of diaphragm 2.

In operation, this microphone is used much in the same manner as the more conventional types. Thus, the operator depresses plunger mechanism 11 prior to speaking, and the spoken signal that is directed toward mouth piece 20 impinges upon diaphragm 2 to set up certain equivapreciable, shutter 18 can be moved to close off chamber 13. Another important feature of the invention lies in the fact that only a minimum portion of the drive rod extends through chamber 13 in which it may be subjected to the restraints or physical injuries already discussed. Also, partition wall 15 protects motor coils 6 and the armature from these influences. In military applications the present microphone is particularly valuable because the possibility of salt spray and other foreign matters aflfecting its functioning parts is reduced to a Further, it should be noted that, in addition to the many functional improvements noted above, the actual structure of the microphone which permits their obtainment is usually simple and entirely practical, and these phones have been constructed and successfully used under very adverse conditions.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A microphone comprising a cup-like casing, a diaphragm mounted transversely across and closing the open end of said cup-like casing, a partition wall spaced inwardly of said diaphragm and extending transversely across the casing for forming with said diaphragm and the casing wall a closed chamber, a generator mounted in the casing interiorly of said partition wall, and an elongate drive-rod inter-connecting the generator and the diaphragm and having its outer end extending through the sealably supported in the central portion of said partition wall, said partition wall being rigid and conical and having its apex forming said drive-rod supporting proximity to the diaphragm that only a relatively small lent vibrations in drive rod 4. The vibrations of the extent of the rod projects through said closed chamber, whereby the remaining elongate extent of said rod is protectively disposed in said casing interiorly of said partition. 2. A microphone comprising a cup-like casing, a diaphragm mounted transversely across and closing the open end of said cup-like casing, a partition wall spaced inwardly of said diaphragm and extending transversely across the casing for forming with said diaphragm and the casing wall a closed chamber, a generator mounted in the casing interiorly of said partition wall, said chamber being provided with a plurality of openings formed in a peripherally-spaced radially-directed arrangement about the casing wall, a rotatable shutter for adjustably closing said openings, and an elongate drive-rod interconnecting the generator and the diaphragm and having its outer end extending through and sealably supported in the central portion of said partition wall, said central drive-rod supporting portion of said partition wall being disposed in such close proximity to the diaphragm that only a relatively small extent of the rod projects through said closed chamber, whereby the remaining elongate extent of said rod is protectively disposed in said casing interiorly of said partition wall.

3. A microphone according to claim 2 in which said partition wall is rigid and conical with its apex forming said drive-rod supporting portion.

References Cited in the file of this patent UNITED STATES PATENTS 1,767,546 Mueller June 24, 1930 1,952,167 'Hasbrouck Mar. 27, 1934 2,358,099 Polk Sept. 12, 1944 2,400,281 Anderson May 14, 1946 2,517,138 Seabert Aug. 1, 1950 2,787,671 Grosskopf et al. Apr. 2, 1957 

